The present invention relates to a signal handling device for enabling data transmission between a plurality of position measuring devices and a master unit. The present invention also relates to an intelligent slave unit for co-operation with the signal handling device, and to a position monitoring system including a signal handling device, an intelligent slave unit and a plurality of position measuring devices. The present invention further relates to a method for enabling data transmission between a plurality of position measuring devices and a master unit, and to a computer program for performing the method.
In many industrial applications there is a need to monitor the movement of a plurality of movable parts. Such monitoring requires the delivery of a number of position signals to a master unit. The master unit may operate to control actuators causing the movement.
The position signals are generated by position measuring devices, i.e. devices for generating a signal indicative of a position. Optoelectrical position measuring devices include an encoding disc that has an optically readable pattern. The disc pattern is read by one or more detectors which each deliver an electric signal in relation to the amount of light that is received in the detector, so that movement of the encoding disc in relation to the detector will be indicated by changes in the electric signal.
The encoding disc includes a periodic pattern, such as a plurality of light and dark fields of mutually the same size, for instance. When the encoding disc is turned or rotated, the change between dark and light fields can be detected and a change in angle thus determined. Some position measurement devices provide a position signal comprising a plurality of pulse signals, where the state of the pulse signals at an instant of time defines the absolute position of the encoding disc in relation to the detector. These position measuring devices are also referred to as absolute encoders.
U.S. Pat. No. 5,687,103 describes a position measuring device having a memory in which specific parameters of the position measuring device are kept. These parameters can be sent on a data line to a processing unit.
The present invention addresses the problem of improving performance of a position monitoring system, or a control system, using a plurality of position measuring devices, and reducing the costs for such a system.
According to an exemplary embodiment of the present invention this problem is addressed by a signal handling device for enabling data transmission between a plurality of position measuring devices and a master unit. The signal handling device includes a main communications port for communicating with a master unit via a data bus; a measurement port for communicating with a position measuring device; an extension port for connection to an intelligent slave unit so as to enable communication with a plurality of position measuring devices via the said slave unit; and an intelligent data processing unit capable of managing data traffic between the main communications port, the measurement port and the extension port.
This solution provides the advantage that a plurality of position measuring devices can be connected to the data bus via a single main communications port. Thereby the master is enabled to communicate with a plurality of position measuring devices using a single address on the data bus, an advantageous feature which reduces the number of position request messages the master has to send for receiving position values from a plurality of position measurement devices. Hence, it is possible to increase the transmission capacity of the bus, in terms of number of transmitted position values, since a plurality of position values can be requested in a single message, and likewise a single response on the bus can include plural position values.
The above mentioned problem is also addressed by an intelligent slave unit for enabling data transmission between a plurality of position measuring devices and a signal handling device of the type described above. The slave unit includes a slave communications port suitable for coupling to an extension port of a signal handling device; a measurement port for communicating with a position measuring device; an extension port for connection to an additional intelligent slave unit so as to enable communication with additional position measuring devices via the additional intelligent slave unit; and a slave data processing unit capable of managing data traffic between the slave communications port, the measurement port and the extension port.
Since each slave unit is provided with an extension port to which another slave unit is easily connectable this solution provides a very high versatility. Additionally this solution makes it possible for the main module to order all slave units to take a measurement sample virtually simultaneously, and to thereafter process the measurement values in parallel.
The above mentioned problem is also addressed by a method for enabling data transmission between a plurality of position measuring devices and a master unit using a signal handling device having a communication port. The method comprises the steps of:
communicating with a master unit via a data bus coupled to the communications port;
communicating with a position measuring device via a measurement port;
enabling communication with a plurality of additional position measuring devices via an extension port; and
managing data traffic between the communications port, the measurement port and the extension port such that a plurality of position values can be communicated via the data bus in a single message.
The above mentioned problem is also addressed by a computer program product, loadable into a digital memory of a signal handling device; comprising software code portions for performing the above mentioned method when said program is run on a data processing unit of a signal handling device. The term xe2x80x9crun on a data processing unitxe2x80x9d means that the computer program plus the data processing unit carries out a method which may be of the kind described above. The term xe2x80x9cloaded into a digital memory of a signal handling devicexe2x80x9d means that the signal handling device programmed in this way is capable or adapted to carrying out a method which may be of the kind described above.
The above mentioned problem is also addressed by a computer program product loadable medium, for use with a slave unit.
An aspect of the present invention relates to the problem of reducing the set-up time required by an operator when installing or upgrading a position monitoring system, or a control system, using a plurality of position measuring devices. More specifically this aspect of the present invention relates to the problem of reducing the set-up time required by an operator when adding a position measuring device to a position monitoring system.
The present invention also addresses the problem of eliminating erroneous set-up of a position monitoring system using a plurality of position measuring devices.
The present invention also addresses the problem of facilitating the maintenance of control systems that include movement or position determining encoders.
The present invention furthermore addresses the problem of reducing the cost for installing or upgrading a position monitoring system, or a control system. This problem is addressed by a signal handling device as defined above, wherein the first extension port of the signal handling device has a pre-assembled connector for enabling a releasable plug-in connection of a slave unit thereto. The slave unit also has an extension port which is also provided with a pre-assembled connector of the same physical constitution.
This solution enables an operator to achieve the set-up in a less complex manner since an additional position measuring device is added by the simple measure of plugging a pre-assembled connector, attached to a slave unit/position measuring device, into a corresponding mating connector of an available extension port.
These problems are also addressed by a computer program product which includes a computer readable arrangement causing a signal handling device to cooperate with any connected slave unit so that a newly connected slave unit is automatically provided with an address to which it should respond.
These problems are also addressed by a computer program product which includes a computer readable arrangement causing a data processing unit to transmit a parameter information request to a connected slave unit for obtaining information about any connected measuring device and a computer readable program arrangement causing a data processing unit to receive such parameter information from a connected slave unit, and forward it to the communications port for delivery to a master. The forwarding of the parameter information to the communications port advantageously simplifies the set-up procedure performed by an operator since it enables the operator to verify the correctness of the set-up in a very quick and efficient manner. The operator may, for example, compare the parameter information thus presented on the masters display with the parameter information, such as serial number and model type, written on the outside of the connected measurement device. In this manner, the operator can easily verify that the set-up is correct and a newly added measurement device complies with the specifications of the position monitoring system, or a control system.